1. Field of the Invention
The present invention relates to a spindle motor and a storage disk drive.
2. Description of the Related Art
Some known motors for use in storage disk drives include a bearing mechanism using a fluid dynamic pressure. An example of such a motor is disclosed in JP-A 2003-56555 and includes a bracket, a shaft, a rotor, and two thrust plates. A lower end of the shaft is fixed in a central opening of the bracket. The rotor includes a sleeve portion in which the shaft is inserted. The sleeve portion is supported to be rotatable with respect to the shaft through a lubricating fluid. Each of the two thrust plates is fixed to an outer circumferential surface of the shaft through press fit and adhesion in the vicinity of a separate end opening of a through hole of the sleeve portion. A thrust bearing portion is defined between an upper portion of the sleeve portion and one of the thrust plates which is arranged above the sleeve portion. The lubricating fluid is arranged in the thrust bearing portion.
An inner circumferential surface of the thrust plate includes a press-fitting surface and an annular recessed portion defined therein. The annular recessed portion is arranged on a lower side of the press-fitting surface. An adhesive is held between the annular recessed portion and the shaft.
Meanwhile, another example of a known spindle motor is disclosed in JP-A 2003-61295 which includes a shaft, ball bearings, a cap, and a rotor hub. An inner race of each ball bearing is fitted to the shaft. The rotor hub is fitted to an outer race of each ball bearing. The cap is arranged above the ball bearings to cover the ball bearings. The cap includes an inner projection and an outer projection, each of which is annular and is arranged to project downward, defined in an inner edge and an outer edge thereof, respectively. The inner projection is fitted to the shaft or the inner race of the upper ball bearing. The outer projection is arranged in a recessed portion defined between the outer race of the upper ball bearing and the rotor hub. A minute gap is defined between the outer projection and the recessed portion. A space defined between the cap and an upper portion of the upper ball bearing is arranged to be in communication with an outside of the motor through the minute gap. The minute gap is arranged to produce a labyrinth seal effect to prevent grease filled into the ball bearings from leaking out of the motor.
Meanwhile, an example of another known motor disclosed in JP-A 08-275435 includes ball bearings, a sleeve fixed to outer circumferential surfaces of the ball bearings, and a cap arranged to cover an upper side of the ball bearings. The cap includes a disk portion and an outer wall portion. The outer wall portion is arranged to extend downward from an outer circumference of the disk portion. A labyrinth seal structure is defined between the outer wall portion and a top portion of the sleeve which is arranged radially inward of the outer wall portion.